This invention is directed to maturing the surfaces of porous metal powder structures to prolong the life of the surface and the underlying structure. Bodies comprised of sintered porous metal bodies can be advantageously used as filters for fluids, such as diesel particulate filters or molten metal filters, substrates for catalysts, such as for automotive, DeNOx, and woodstove combustor applications, as structural building materials, and generally for structures to support needs for high surface area stable surfaces.
Commonly, such structures are combined with catalysts, such as the base metals and/or noble metals, to be introduced into troublesome effluents that must be converted into some other chemical species. Typically, the method of use is accomplished by putting the structure in the exhaust pathway of either organically fueled power plants or in the exhaust pathway of internal combustion engines.
U.S. Pat. No. 4,758,272 discloses a family of one of the compositions contemplated hereunder, and is incorporated herein by reference for all that is disclosed therein. In that inventive effort an iron aluminum alloy was sintered into a hard porous body. In copending U.S. patent application Ser. No. 219,986 filed July 15, 1988, another composition is disclosed. That disclosure is incorporated herein by reference, as filed. In copending U.S. patent application Ser. No. 273,214 now abandoned filed Nov. 18, 1988, an oxide surface is discussed. That disclosure is incorporated herein by reference, as filed.
That various metal powder structures can be batched, extruded and subsequently sintered into hard porous bodies is a technical achievement. For purposes of durability, however, the bodies from these kind of structures must be additionally treated to provide along lived durable product. As used in the proposed environment, bald sintered surfaces of the subject substrates were found to degrade. This is a disadvantage for a number of reasons, not, the least of which is that the surface on the bald sintered structures can be the interface between costly catalysts and the high surface area structure. Should that interface degrade, the catalyst/substrate system would fail.
The present invention is directed to curing the surface of sintered metal powder porous bodies. The curing a controlled densification and oxidation of the surface layer. This surface layer can be up to a couple of microns thick, most preferably from 0.5 to 1 micron. It is important to understand that controlled densification is defined as directed to the oxide layer only. This densified layer provides durability to the surface, but does not subtract from the porosity of the structure. This important feature provides the structure with the porosity common to a high surface area substrate and adds long life consistent with commercial needs.
Advantageously, the curing process results in an oxide film, durable as a protective coating for the underlying structure. Perhaps as significantly, this protective coating provides a durable high surface area interface integral with the underlying structure that is capable of binding various catalysts. A system so formed may then be placed in harsh environments with an added level of confidence that the system will survive.
Essentially, the final structure of the present invention is a synthesis between a metal core and a ceramic outer layer. The prior work in this field contains either a ceramic high surface area substrate or a contorted metal foil subsequently layered with a high surface area coating. The invention, herein, supplants both of these technologies with a porous metal core intimately integral to a high surface area durable surface.